Gonville & Caius College Fellow Dr Michele Simoncelli has been awarded a 2021 EPFL Doctorate Award for his thesis “Thermal transport beyond Fourier, and beyond Boltzmann”.

The award — established in 1993 to distinguish work performed during an outstanding doctoral thesis at EPFL and to encourage particularly qualified researchers — was presented to Michele, a former doctoral student at the Theory and Simulation of Materials (THEOS) lab of Professor Nicola Marzari and NCCR MARVEL, as well as two other winners at a ceremony in Lausanne on Monday night.

Every year the award is presented to three doctoral theses, chosen across all disciplines (over 400 dissertations were presented at EPFL in 2020-2021). The prize honours candidates who produce remarkable theses in terms of originality, the impact of results as measured by publication in one or several international journals and the presentation of the work. 

“I’m very happy to receive it, but in general science is a collaborative effort," Michele said.

"I had the chance to work with extremely brilliant scientists during my PhD. In particular, my PhD advisor Professor Nicola Marzari deeply supported and trusted me, and I also collaborated fruitfully with Professor Francesco Mauri and Dr Andrea Cepellotti. I would like to thank them for the very enriching scientific journey. I also had a great time at EPFL, and this of all contributed to the work I was able to do.”

His thesis presents a unified microscopic, quantum equation that describes heat conduction in crystals, glasses, and anything in-between on an equal footing. It predicts, correctly and in agreement with experiments, thermal conductivity in crystals, glasses, and, most importantly, in the mixed regime of complex crystals with ultra-low or glass-like conductivity. This was a significant first — no transport equation had so far been able to describe all of these materials simultaneously.  

The formulation is relevant for several technological applications: it has been applied in the aerospace industry and in the field of renewable energy, setting the stage for the systematic engineering of thermal barrier coatings and the enhancement of the efficiency of devices used for thermoelectric conversion of waste heat into electricity. 

The thesis also showed how in the crystalline regime such a microscopic transport equation can be coarse-grained into a set of “viscous heat equations” that generalize the macroscopic heat equation formulated by Fourier in 1822. These viscous heat equations account for both heat diffusion and heat hydrodynamics, and rationalise the recent discovery of heat transfer via temperature waves in graphitic devices. It therefore promises to be useful in the design of next-generation electronic devices, where heat is the main limiting factor for miniaturisation and efficiency. 

Dr Simoncelli is currently working in the Theory of Condensed Matter Group in the Cavendish Laboratory. His primary focus is on the development of the theoretical and computational framework needed to understand and engineer transport phenomena (eg charge, heat, spin transfer) occurring in solids and exploited in industrial applications including renewable energy harvesting and conversion, thermal barriers for aerospace, and electronics.

This article has been partially reproduced from the NCCR MARVEL website.

Additional information: 

An article on the paper "Unified theory of thermal transport in crystals and glasses", published in Nature Physics.  

An article on the paper "Generalization of Fourier’s law into viscous heat equations", published in Physical Review X. 

An additional paper, "Wigner formulation of thermal transport in solids", stemming from Simoncelli’s thesis, was recently published in Physical Review X.